On Thu, Jul 22, 2021 at 11:29 AM Tom Lane <t...@sss.pgh.pa.us> wrote: > As a thought experiment to prove that this is an issue, suppose that > somebody invented an unsigned integer type, and made the cast from > regular int4 follow the rules of a C cast, so that e.g. -1 becomes > 2^32-1. Given that, an ALTER TYPE from int4 to the unsigned type > could skip the heap rewrite. But we absolutely would have to rebuild > any btree index on the column, because the sort ordering of the two > types is different. OTOH, it's quite likely that a hash index would > not really need to be rebuilt. So this is a real can of worms and > we've not cared to open it.
I agree that it doesn't follow in general. I think it does in the case of timestamp and timestamptz, because I don't think either the choice of time zone or the fact that we're reckoning relative to a time zone can change which of two timestamps is considered earlier. However, I think the only infrastructure we have for proving that is to look to see whether it's the same operator family in both cases. Because timestamp_ops and timestamptz_ops are separate, that doesn't help here. -- Robert Haas EDB: http://www.enterprisedb.com
